Atomic-oxygen undercutting of protected polymers in low earth orbit

Hydrocarbon-based polymers that are exposed to atomic oxygen in low Earth orbit are slowly oxidized into volatile gases, which results in their erosion. Atomic-oxygen protective coatings that are both durable to atomic oxygen and effective in protecting underlying polymers have been developed. However, scratches, pin window defects,. polymer surface roughness, and protective coating layer configuration can result in erosion and potential failure of protected thin polymer films even though the coatings are themselves atomic-oxygen durable. Issues are presented that cause protective coatings to become ineffective in some cases yet effective in others because of the details of their specific application. Observed in-space examples of failed and successfully protected materials using identical protective thin films are discussed and analyzed. Ground laboratory atomic-oxygen testing was conducted and compared with water vapor transport analyses from a previous study of protective coatings on Kapton(R) (polyimide), which indicates that vapor-deposited aluminized films are not as protective as sputter-deposited silicon dioxide films because of a greater number of pin window defects. Computational modeling was conducted and indicates that atomic-oxygen atoms trapped between the front and back surface aluminized films cause accelerated undercutting damage.